Same as Modern variant, basically. They can move over both provinces & sea spaces (making them a real bane to stalemate lines). They cannot capture supply centers, but they can blockade them, which causes the center to not count towards the supply center count of the power that owns it as long as it is blockaded. I'm unsure of whether planes will be powerful enough, so I may change it so that the power that owns the blockaded center will have to actually re-enter it afterwards to end the blockade.